With the extensive application of communication technology and for increasing the speed of uploading and downloading of data on mobile devices, long term evolution (LTE) communication technology, the next generation of communication systems, has been rapidly applied to people's lives. In response to the development of 4G communication systems, not only the original 2G/3G but also the new 4G communication bands are required to be compatible; therefore, the number of antennas in the mobile device and the corresponding bandwidth must be increased.
In addition, because today's mobile device is developed to have a compact size, the design of its antenna must also consider the accommodating space. Therefore, how to allow the antenna in a limited accommodating space to cover a wider range of bandwidth is an urgent issue needed to be solved.